So one of my 3/4 water valves on my main line that goest to the water heater was leaking out the valve stem shaft. When looking at that I noticed that there was a pin hole leak on the side of the brass valve. I cleaned it off and waited a few months and sure enough more 'puss' and crud is coming out. There is a small bubble of gunk on the right side of the bleed valve:

I cut off the valve and switched it with a ball valve today and check out the inside:

What the heck is all that crap? My house is 9 years old and that looks a bit off if you ask me. Could the brass be corroding from the inside out? Is that leftover Flux? Is this normal or no?

Seeing the inside of my water lines sure makes me happy I use water filters!

it almost looks like a seal filler. that gunk looks like my old emersion heating copper pipes. the pipes had a black substance in them to stop the pipe corroding. as we checked the all the 30 yrs+ old piping we realised that the system had never been cleaned/flushed. all this yellow slime like stuff came out. now we now what was causing the pressure issue and the random loud clunk from time to time. it turns out this gunk was in fact a sealing substance used many years ago to save money on replacing all damage pipes. the excess wasn't flushed out and started to clog the pipes. could well be the same stuff you have there?